To keep a wearer safe and comfortable, footwear is called upon to perform a variety of functions. For example, the sole structure of footwear should provide adequate support and impact force attenuation properties to prevent injury and reduce fatigue, while at the same time provide adequate flexibility so that the sole structure articulates, flexes, stretches, or otherwise moves to allow an individual to fully utilize the natural motion of the foot
Conventional articles of athletic footwear generally include two primary elements, an upper and a sole structure. The upper is secured to the sole structure and forms a void on the interior of the footwear for comfortably and securely receiving a foot. The sole structure is secured to a lower portion of the upper and is positioned between the foot and the ground. The sole structure generally incorporates multiple layers that are conventionally referred to as an insole, a midsole, and an outsole. The insole, or sockliner, is a thin, compressible member located within the void and proximate a lower surface of the foot to enhance footwear comfort. The midsole, which is conventionally secured to the upper along the length of the upper, forms a middle layer of the sole structure and serves a variety of purposes that include attenuating ground (or other contact surface) reaction forces to lessen stresses upon the foot and leg; controlling potentially harmful foot motions, such as over pronation; and beneficially utilizing such ground reaction forces for more efficient toe-off. The outsole forms a ground-engaging portion (or other contact surface-engaging portion) of the sole structure, and is formed from a durable and wear-resistant material that includes texturing to improve traction.
The conventional midsole is primarily formed from a resilient, polymer foam material that extends throughout the length of the footwear, often by way of a molding process. The properties of the polymer foam material in the midsole are primarily dependent upon factors that include the dimensional configuration of the midsole and the specific characteristics of the material selected for the polymer foam, including the hardness or density of the polymer foam material. By varying these factors throughout the midsole, the relative stiffness and degree of ground reaction force attenuation may be altered to meet the specific demands of the activity for which the footwear is intended to be used. In addition to polymer foam materials, conventional midsoles may include, for example, one or more fluid-filled bladders (e.g., filled with air or other gasses) and moderators.
Midsoles may be formed with sipes, which are vertically extending slots or recesses formed in the midsole that form sole elements throughout the midsole and an articulated configuration that provides flexibility for the footwear. The sipes may be formed during a molding process used to form the midsole, or they may be cut into the midsole with a hot knife or other suitable members after the midsole has been formed.
A mold used to form a midsole may include blades extending upwardly from a bottom portion of the mold, with the blades defining the sipes within the material used to form the midsole. In some footwear the sipes may be relatively narrow and relatively deep, in which case the blades used to make such sipes may be susceptible to breakage.
It would be desirable to provide a mold and method of manufacturing footwear with sipes that reduces or overcomes some or all of the difficulties inherent in prior known devices. Particular advantages will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of certain embodiments.